Scientists develop green concrete that recycles twice the coal ash

Dr. Chamila Gunasekara holds a sample of the low-carbon concrete. Credit: Michael Quin, RMIT University.

Researchers at RMIT University have created a revolutionary type of low-carbon concrete that can recycle twice as much coal ash as current standards.

This new concrete not only cuts the amount of cement required in half but also performs exceptionally well over time.

In 2022, over 1.2 billion metric tons of coal ash were produced by coal-fired power plants.

In Australia alone, coal ash accounts for nearly a fifth of all waste and will continue to be abundant for years, even as the country transitions to renewable energy sources.

Meanwhile, cement production is responsible for 8% of global carbon emissions, and the demand for concrete is rapidly increasing.

To address these challenges, engineers at RMIT University have partnered with AGL’s Loy Yang Power Station and the Ash Development Association of Australia to replace 80% of the cement in concrete with coal fly ash.

This is a significant improvement over existing low-carbon concretes, which typically replace only up to 40% of their cement with fly ash.

Dr. Chamila Gunasekara, the project lead from RMIT’s School of Engineering, explains that the addition of nano additives modifies the concrete’s chemistry, allowing more fly ash to be used without compromising its performance.

The team’s research has also found new opportunities in using lower-grade “pond ash,” which is taken from coal slurry storage ponds at power plants.

This type of ash has been largely overlooked in construction due to its different characteristics compared to fly ash. However, lab studies have shown that the new concrete can effectively use pond ash with minimal pre-processing.

Large concrete beam prototypes made from both fly ash and pond ash have met Australian Standards for engineering performance and environmental requirements.

Dr. Gunasekara highlights the potential of pond ash as a resource for cement replacement. “There are hundreds of megatonnes of ash wastes sitting in dams around Australia, and much more globally.

These ash ponds risk becoming an environmental hazard, and the ability to repurpose this ash in construction materials at scale would be a massive win.”

In addition to developing the new concrete, the RMIT team has also created a pilot computer modeling program to predict its long-term performance.

This program, developed in partnership with Dr. Yogarajah Elakneswaran from Hokkaido University, uses a physics-based model to forecast how the new concrete mixtures will perform over time.

Dr. Yuguo Yu, an expert in virtual computational mechanics at RMIT, explains that this model allows the team to optimize the concrete mixes based on numerical insights.

The modeling shows how the quick-setting nano additives in the concrete act as performance boosters during the early stages of setting, compensating for the slower-setting fly ash and pond ash. This increases the density and compactness of the material, enhancing its overall performance.

This innovative approach has been detailed in the journal Cement and Concrete Research and represents a major step towards using digital simulations in infrastructure design and construction.

By leveraging this technology, the RMIT team hopes to encourage local councils and communities to adopt this novel low-carbon concrete for various applications, paving the way for more sustainable construction practices.

Source: RMIT University.